1. Field of the Invention
The present invention relates to the improvement of a data circuit-terminating equipment with a power source device.
2. Description of the Related Arts
A data communication system for connecting the data terminal equipments (hereinunder referred to as "DTE") of personal computers or the like through a telephone circuit and for transmitting and receiving data between the DTEs has recently been increasingly used.
Modems (modulator/demodulator) 10 are attached to respective DTEs 12 in the data communication system schematically as shown in FIG. 5, and are connected with each other by a telephone circuit 14. The modem 10 is a device for modulating the signal from the DTE 12 to a signal suitable for use by the telephone circuit 14 and for demodulating the signal received from the telephone circuit 14 to a signal suitable for the DTE 12, and plays an important role in a data communication system having the structure such as that shown in FIG. 5. The reference numeral 16 represents an RS232C cable.
The structure of the conventional modem 10 will be explained with reference to FIG. 6.
As shown in FIG. 6, the modem 10 mainly includes a modulation and demodulation circuit 18 for modulating a digital signal supplied from the DTE 12 to a circuit signal, demodulating the received circuit signal to a digital signal of an RS232C type and supplying it to the DTE 12, and a net control unit 20 (hereinunder referred to as NCU) for controlling the connection between the modulation and demodulation circuit 18 and a telephone circuit 14.
The modem 10 is further provided with a two-wire four-wire circuit 22, namely, a circuit for dividing the telephone circuit 14 connected to the terminals 1 and 2 of the NCU 20 into a transmitting circuit and a receiving circuit.
A conventional modem has the above-described structure. This modem is disadvantageous in that since a power source apparatus 24 exclusively for driving the modem is necessary, the miniaturization of a data communication system is difficult.